1. Field of the Invention
The present invention relates to an electric induction furnace and, more particularly, to an electric induction furnace for heating various electrically conductive materials that is adapted to be directly connected to a horizontal mold, while at the same time allowing venting of trapped gases and impurities in the conductive material.
2. Description of the Prior Art
Electric induction furnaces are generally known in the art. Such furnaces are known to be used in various industries for melting various electrically conductive materials, such as brass. Such furnaces are also known to be used as holding furnaces for maintaining various materials in a molten state.
Electrical induction furnaces normally include a single crucible for holding an electrically conductive material and an electric coil; disposed about the crucible. A source of alternating current (AC) electric power is applied to the electric coil which, in turn, induces eddy currents in the electrically conductive material. The induced eddy currents flow in the electrically conductive material to cause internal resistance heating of the material as a result of the material's own resistivity.
The magnitude of the induced eddy currents and, hence, the heating of the electrically conductive material is directly proportional to the square root of the material's resistivity .rho. and inversely proportional to the material's permeability .mu. and frequency of the AC power applied to the electric coil. Thus, the frequency of the AC power applied to the electric coil is selected according to the particular application as well as the properties of the electrically conductive material. For applications for holding furnaces, frequencies between 20 and 300 Hz are known to be used.
Various configurations of such electric induction furnaces are known. In particular, these configurations relate to the orientation of the longitudinal axis of the crucible used for holding the electrically conductive material. In particular, both vertical and horizontal orientations of the crucibles are known. The orientation of the crucible is selected in accordance with the particular process in which it is to be used. For example, in applications where the electric induction furnace is to be used in conjunction with a horizontal casting operation, furnaces with horizontally oriented crucibles are normally selected. However, there are certain problems known to exist with such electric induction furnaces having horizontally oriented crucibles. In particular, the induced eddy currents are known to cause turbulence within the electrically conductive material which effectively creates a type of stirring action within the crucible. Although such stirring action is generally desirable; in furnaces having horizontally configured crucibles, such action also can cause gases to be trapped within the electrically conductive material which can result in voids in the resulting casting.
In addition, there are other problems with some known electric induction furnaces. In particular, in a typical casting operation, a casting mold is normally directly secured to a mounting flange on the holding furnace. In some known applications, changing of casting molds has been known to be relatively difficult.
There are also other problems with known electrical induction furnaces. In particular, as mentioned above, the casting molds are normally secured to a mounting flange on the outside of the furnace. Such an arrangement results in heat loss making the cost of producing the casted products more expensive. In addition, with such an arrangement, it is relatively difficult to control the temperature of the molten material at the mold entry point which can affect the mechanical properties of the resulting casting and result in non-uniform castings.
In addition, such furnaces are known to utilize a single crucible. In the event that this crucible cracks while holding a molten material, the surrounding electrical coil can be damaged. In addition, such crucibles are known to wear and require replacement. Replacement of a crucible in an electric induction furnace having a single crucible is known to be relatively expensive.